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Michael Solar RD50 Workshop CERN 3.- 5.11.2003
CTU Prague RD50 Group
Detector structures on GaAs(Mesa with Guard Rings)
T. Horazdovský, D. Chren, Z. Kohout, M. Solar, B. Sopko ME CTUV. Jurka, E. Hulicius IP ASCR
S. Pospisil IEAP CTU
Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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ContentsMotivation
Structure of detectors
Technology for GaAs detectors
Results
Conclusion
References
Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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MotivationThe structure of detector on SI GaAs substrate was created using Schottky contact.
The properties of the Schottky contact depend on metallization technology.
The diffusion technology eliminate the influence of a substrate material on detector performance.
For more stable properties we made the structure with PN – junction (diffused or epi layer).
Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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Motivation
Diffusion solid-to-solid of Zn or MOCVD epi layer give us possibility to make ohmic contact on P+ side and give further possibility for research of detection structure.
Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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Structure of the detectorsSI GaAs substrate , thick. 500 um
1. P+ (Zn) junction depth (2 – 4 ) umMetallization of P+ (front) side : TiAu (10 nm + 200 nm)Metallization of back side: AuGeNi (200+100+100)nm (Fig.1)
or
2. MOCVD epi layer P+ (C) thickn. 0,5 umMOCVD epi layer N+ (Si) – back sideMetallization of P+ and back side : TiAu (10 nm + 200 nm)
(Fig. 2, 3)
Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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Technology for GaAs detectorsDiffused type
deposition of SiO2 + ZnO layersdiffusion of Zn (solid – to – solid)- bellow 800 °C, in FG
removing of SiO2 + ZnO layers
making a ohmic contact on P+ and N+ side of structure(standard metallization : TiAu, AuGeNi, annealing 400 °C in FG)
separation of detector chips (cutting) - after cutting of the wafer to detector chips (5 x 5 mm) the sides of the chips was prepared
by a special protectiv layer(Protection technology similar as for HV diodes)
Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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Structure of the detectors
AuGeNi
SI GaAs
TiAu
P+ (Zn)
Fig.1:Vertical structure of detectors - diffusion type of structure
Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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Technology for GaAs detectorsMOCVD type without guard ring
deposition of MOCVD epi layer (P+ , dot. C)back side deposition of MOCVD epi layer (N+, dot. Si)
making a ohmic contact on P+ and N+ side of structure(standard metallization : TiAu, AuGeNi, annealing 400 °C in FG)
separation of detector chips (cutting) - after cutting of the wafer to detector chips (5 x 5 mm) the sides of the chips was prepared
by a special protectiv layer
Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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Structure of the detectors
Fig.2: Vertical structure of detectors - MOCVD epi type of structure
TiAu
SI GaAs
TiAu
MOCVD P+ (C)
N+ epi (Si)
Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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Technology for GaAs detectorsMOCVD type with guard ring
deposition of MOCVD epi layer (P+ , dot. C)back side deposition of MOCVD epi layer (N+, dot. Si)
making a ohmic contact on P+ and N+ side of structure- standard metallization : TiAu
etching of the metallization to designed pattern
following etching of GaAs (patterned metallization serves as etching mask) to form MESA structure
This structure had not passivated surface
Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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Structure of the detectors
TiAu
SI GaAs
TiAu
MOCVD P+ (C)
N+ epi (Si)
Fig.3: Vertical structure of detector with guard ring - MOCVD epi type of structure
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ResultsI-V characteristic - diffused type
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Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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Resultscip1 45V
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cip1 90V
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cip1 132V
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Am241Pu239
Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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Results I-V characteristic - MOCVD type
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Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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Results
cip2 133V
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cip2 47V
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cip2 91V
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Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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Results
Fig.4: The photo of MESA type detectors with guard rings
Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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Results I-V characteristic - MESA type (MOCVD)
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Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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Results50V
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Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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Conclusions
•Experiments show the ability of described technology to prepare functional detectors on GaAs
•The results show the MESA type has better leaking current in comparison with “surface preserved” type even the guard rings were not biased
•In near future we will study:- the influence of guard ring bias on the detector properties,- the spectra using gamma and rtg sources,- the influence of protective materials on I-V characterics
Michael Solar RD50 Workshop CERN 3.- 5.11.2003
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References1. C.R.M.Grovenor: Structure of the Au/Ga As interface, EMIS Datareview RN=11126, September 1989
2. B.Tuck, T. Harrison: Diffusion of Zn in Ga As, EMIS Datareview RN=15150, February 1990
3. J.Ivančo at all: Semi-insulating Ga As – based Schottky contacts for the detector of Ionising radiation: An effect of the interface treatment,6th International Workshop on GaAs and related compounds, Praha – Průhonice, June 22-26,1998
4. P.J.Selin at all : Characterisation of X-ray detectors fabricated from thick epitaxial Ga As NIM A 460 (2001) 159-164
Michael Solar RD50 Workshop CERN 3.- 5.11.2003
CTU Prague RD50 Group
Thank you for your attention
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